1. Field of the Invention
The present invention relates to a diene block polymer having an improved cold flow, superior physical properties, and processability in various applications and to a polymer composition having as a principal component the diene block polymer. More specifically, it relates to a block polymer comprised of a resinous polybutadiene block having 80 to 93% trans units and a rubbery diene block and to a polymer composition having the same as one of its principal components.
The diene block polymer and polymer composition of the present invention are diene rubbers with improved cold flow and are suited for all types of applications where diene rubbers have been used in the past. The polymer composition of the present invention, which includes the block polymer, is a raw rubber which gives a composition which has excellent strength, wear resistance, and processability. Having these functional features enables it to be used for tire treads, sidewalls, carcasses, and other tire parts used on trucks, buses, construction vehicles, passenger cars, motorcycles, and bicycles, shock absorbing rubber, belts, and other auto parts, industrial parts, and other rubber applications. Further, it may be excellently used in high impact polystyrene resin applications.
2. Discussion of the Related Art
There is known a polybutadiene with high trans units, e.g., 80 percent or more trans units. As the methods for the production of the same, the following three methods are known: (1) The method comprising the use of a Ziegler catalyst comprised of a transitional metal compound and an organic metal compound, (2) the method comprising the use of an anionic polymerization catalyst having as a principal component an alkaline earth metal compound, and (3) the method comprising the use of a catalyst having as a principal component a rare earth metal compound.
The method of the above-mentioned (1) uses as principal components transitional metal compounds of nickel, cobalt, titanium, vanadium, etc., and enables the polymerization to form a polymer having a high degree of stereospecificity. For example, as a polymerization method of butadiene using titanium metal, there is the method of use of a carrier of a tetravalent titanium metal compound with magnesium halogenate (Japanese Unexamined Patent Publication (Kokai) No. 51-67387). Further, in the case of using a vanadium compound as the principal component, it is possible to obtain a polymer having a very high trans content. For example, methods are known for polymerizing isoprene using a composite catalyst of a tetravalent vanadium halogenate and organic aluminum (Japanese Unexamined Patent Publication (Kokai) No. 50-36585) and further for polymerizing isoprene using a composite catalyst comprised of a trivalent or tetravalent vanadium compound and organic aluminum and tetravalent titanium compound (Japanese Unexamined Patent Publication (Kokai) No. 49-29386 and Japanese Unexamined Patent Publication (Kokai) NO. 50-122586) etc.
In the above method of (2), there are examples of the polymerization of butadiene using as principal components, barium, strontium, and calcium compounds, e.g., barium-di-tert-butoxide and organic lithium (U.S. Pat. No. 3,629,213) or barium-di-tert-butoxide and organic magnesium (Japanese Unexamined Patent Publication (Kokai) No. 52-48910), etc. Further, there is known the method of the polymerization of a conjugated diene using an organometallic compound of an organic compound of barium or strontium and organolithium and IIB or IIIA metal, etc.
In the above method of (3), there are known composite catalysts using rare earth metal compounds as the main catalysts and organomagnesium compounds as the secondary catalysts. For example, Japanese Unexamined Patent Publication (Kokai) No. 59-1508 and U.S. Pat. No. 4,689,368 proposes a method using rare earth metal such as Di, Nd, Pr, and other varsaticates or special .alpha.- and .gamma.-diketone complexes to produce high trans polybutadiene and a diene block polymer comprised of high trans block and high cis block.
Further, Japanese Unexamined Patent Publication (Kokai) No. 61-19611 and GB 2161169 proposes compounds of cerium and europium, and Japanese Unexamined Patent Publication (Kokai) No. 61-97311 proposes polymerization using the same type of catalysts using compounds of lanthan as the main catalysts, which produce with high efficiency polybutadiene with high trans units.
A process for polymerizing butadiene to form polybutadiene having trans units of up to 60 percent using an organolithium compound as a catalyst is also known. Details of the process are disclosed in, for example, "The Stereo Rubber", edited by William M. Saltman, 1977, chapter 4. It is reported therein that by polymerizing butadiene using lithium metal or organolithium compounds under a nonpolar solvent, it is possible to obtain a polymer having 48 to 50% trans units and that the addition of a polar compound to this system results in a rise in the 1,2-bonds and a decline in the 1,4-bonds (cis units and trans units).
Further, there have been proposed a polymer having as one of its components a block polymer of a high trans butadiene copolymer and high vinyl bond butadiene polymer and a method for production of the same (Japanese Unexamined Patent Publication (KoKai) No. 61-238845 and U.S. Pat. No. 4,669,518).
According to that specification (claim 1), there was proposed the following:
"A composition including a rubber polymer selected form the group consisting of the following: PA0 "The method for production of the HTSBR-b-HVSBR involves the copolymerization of butadiene and styrene in cyclohexane to a conversion of about 60 to 95%, preferably about 85% by using a barium salt of alcohol combined with an organomagnesium compound and organoaluminum compound or organomagnesium/organoaluminum complex for formation of HTSBR (block A) followed by addition of sodium (preferably), potassium, or rubidium alcoholate or their mixture and a strong Lewis acid or, if desired, an additional monomer for formation of the HVSBR (block B). The SBR produced has styrene units with a dominant random distribution in each block. The high content of trans-1,4 positions in block A causes somewhat of a crystallinity, as observed by differential scanning calorimetry (DSC) and the crystal melting point, but the crystal melting point can be lowered to close to room temperature (about 25.degree. C.) or lower by adjustment of the trans-1,4 content and styrene level. The polymers formed have reduced ordinary temperature flow and superior processability".
I. A diblock copolymer of a high trans copolymer and high vinyl polymer, PA1 II. A blend of a high trans copolymer and high vinyl polymer, and PA1 III. A blend or mixture of a diblock copolymer of a high trans copolymer and high vinyl copolymer, a high trans copolymer, and a high vinyl polymer, wherein
a) the high trans copolymer is a copolymer of butadiene-1,3 and at least one copolymerizable monomer selected from the group consisting of styrene and isoprene, which has a Tg of less than about -70.degree. C., which has a total content of about 75 to 85% of trans units and up to about 8% of vinyl units in the butadiene segments, and which accounts for 25 to 80% by weight of the composition, PA2 b) the high vinyl polymer is at least one polymer selected from the group consisting of copolymers of homopolybutadiene, at least one monomer selected from the group composed of styrene and isoprene, and butadiene-1,3, which has a Tg larger than about -70.degree. C. and not exceeding about -35.degree. C. and which has about 40 to 80% vinyl units in the butadiene segment, PA2 c) further, in the composition, the total amount of styrene and/or isoprene is about 5 to about 20% by weight and the total amount of vinyl units is about 30 to 60%."
Further, a method for producing this polymer composition is given in claim 9. The gist of the same is given in the specification as follows:
However, in each of the above-mentioned methods and polymers, the activity of the polymerization giving trans copolymer portion in the first stage is extremely low and further, the second stage polymerization is inferior in living ability and gives rise to an unpreferably enlarged distribution of molecular weight, a reduced ratio of block polymers such as HTSBR-b-HVSBR in the resultant polymer composition, and an increased ratio of HTSBR homopolymers. Further the resultant polymer has a higher Tg value compared with the homopolymer due to the first block being a high trans copolymer. The Tm value (crystal melting point) is also low or else nonexistent. The superior physical properties of rubber given by the high trans block portion (improved cold flow, hardness, improved modulus, improved wear resistance, etc.) are insufficiently exhibited and, conversely, the increase of the high trans copolymer portion to an amount higher than necessary causes a decline in the heat resistance and low temperature performance and thus is not preferred.
Accordingly, the objects of the present invention are to eliminate the above-mentioned problems of the prior art and to provide a diene block polymer having an improved cold flow, excellent physical properties, and workability.
Another object of the present invention is to provide a polymer composition containing the above-mentioned diene block polymer.
Other objects and advantages of the present invention will be apparent from the following description.